That is a great question.  Here are the directions for baking our Betty Crocker Angel Food cake mix in a 13 x 9" pan.  You can use metal or glass for this recipe.  Happy baking!  

13x9x2 Rectangular Pan Directions

Betty Crocker® Angel Food White 1-Step

YOU WILL NEED                1 1/4 CUPS WATER

1.  MOVE oven rack to middle position.  HEAT oven to 350°--metal or glass pan. 

2.  BEAT cake mix and water in large (4-quart) glass or metal bowl on low speed 30 seconds; scrape side of bowl.  Beat on medium speed 1 minute.  Pour into ungreased pan. 

3.  SPREAD batter evenly in rectangular pan.  

4.  BAKE 13"x9"x2" rectangular pan 35-45 min until cracks feel dry and crust is dark golden brown..  

5.  COOL rectangular pan upside down, resting each corner on can of equal height. 

High Altitude (3500-6500 ft):  Prepare as directed--except stir 1/4 cup allpurpose flour into cake mix (dry).  Increase beating time on medium speed to 2 min.  Bake rectangle 37-43 min

Success Tips for Angel Food Cake:

    For best cake height, use ungreased pan so batter can cling to side(s) during baking.  Cool cake upside down.

    To prevent batter from overflowing when baking in loaf pans, fill pans no more than 2/3 full.

    To ensure cake stays in pan during cooling, do not underbake.

    To prevent pressing down and crushing cake, cut in a gentle sawing motion with sharp, thin serrated or electric knife.

    To maintain freshness, store cake in airtight container.